# Purpose of using polyphase filter bank (PFB)

What is the advantage of using a polyphase filter bank (PFB) for spectral analysis over just using the FFT? In the standard "critically sampled" uniform DFT filterbank, the polyphase decimation/filtering is followed by an $M$-point DFT block, which implements the last step of the PFB in a computationally efficient manner using the FFT.

If you have to do an FFT anyways, why bother with the PFB? Is the reason that I can choose a custom prototype low-pass filter on the front-end? Are there some computational savings I'm missing out on?

EDIT: If comparing this to a bank of quadrature downconverters, what is the point of using a PFB if the FFT is the same mathematically? It can't be the delay of $N$ samples requried to fill up an FFT block because the decimated branches have $1/N$ the rate, which means you will be waiting the same amount of time on average with either approach. What am I missing?